The intention of this work has been twofold: (1) to create a scintigraphic imaging system capable of all forms of nuclear tracer imaging in small animals and (2), to use this system to study tracer biodistributions and to study organ function during various interventions. During this reporting period the second goal of this program was realized, namely successful SPECT imaging of small animal organs. This goal follows creation of a high resolution planar imaging system developed during the previous reporting periods. These technical achievements were paralleled by use of this system to image new compounds in the rat and guinea pig brain such as I-123 labelled QNB, a muscarinic receptor ligand and I-125 labelled loxy, a cyclo-foxy analog. In addition, Tc-labelled compounds for imaging cerebral blood flow, lung perfusion, myocardial blood flow and cardiac function were also evaluated successfully.